This project is the first human study to examine the effects of widely used perfluoroalkyl substances (PFAS) on nonalcoholic fatty liver disease (NAFLD), using the gold standard of liver biopsies for disease diagnosis and liver-specific and plasma metabolomic measures to examine biological mechanisms linking PFAS to liver disease. We are examining this hypothesis in a novel study design using liver and plasma samples from obese adolescents undergoing bariatric surgery. The project addresses a critical gap in our current understanding of etiology of the rapid increase in occurrence of NAFLD in youth and could ultimately lead to new strategies for treatment and prevention.